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Each year in the United States, approximately 400 deaths are attributed to excessive natural heat; these deaths
are preventable (1). This report describes heat-related deaths in Missouri, New Mexico, Oklahoma, and Texas when
elevated temperatures were recorded for several consecutive days during July--August 2001; summarizes heat-related deaths in
the
United States during 1979--1999; and presents risk factors and preventive measures associated with heat-related illness
and death, especially in susceptible populations.

In late July 2001, the National Oceanographic and Atmospheric Association (NOAA) reported temperatures averaging 5º
F (-15º C)--10º F (-12º C) above normal in the southern plains states
(2). The intense heat and humidity prompted
NOAA's National Weather Service to issue heat advisories* in Missouri, New Mexico, Oklahoma, and Texas
(2; Missouri Department of Health and Senior Services, personal communication 2002). During July--August 2001, a total of 95 deaths was
attributed to excessive natural heat in the affected states. Provisional mortality statistics were obtained from the vital statistics section
of each state, and information about underlying cause of death, age, sex, date of death, and contributing causes were
provided. Peak mortality occurred during the reported 8-day heat advisory period (Figure 1). Six (6%) deaths occurred among
children aged <4 years and 42 (41%) among persons aged
>75 years; 69 (73%) deaths occurred among males.

Case Reports

Case 1. In Oklahoma in mid-July 2001, a man aged 29 years was found disoriented and wandering in a
commercial parking lot. He apparently had fallen and had abrasions on his knees and a broken tooth. In the emergency department,
he was semiconscious but combative. His rectal temperature increased from 105.4º F (40.7º C) to 107.8º F (42.1º C) in
<1 hour. Despite medical treatment for hyperthermia, he was pronounced dead 22 hours after being found. Laboratory tests
at autopsy were positive for cocaine and alcohol. The medical examiner attributed the cause of death to heat-related illness.

Case 2. In Oklahoma in mid-July 2001, police were called to check on a man aged 62 years with a history of
alcoholism, heavy smoking, and poor diet who had not been seen for 7 days. The man was found dead by the police in his home,
which was very hot; an ambient temperature was not recorded. A fan and air-conditioning unit in the home were in working
order but turned off. Postmortem blood alcohol level was 0.07%. Following an autopsy, the death was attributed to hyperthermia.

Case 3. In Texas in late July 2001, a boy aged 2 years was found in a motor vehicle with the windows rolled up for
an undetermined length of time. The boy had locked himself in the car and could not get out. The temperature inside the
car was not measured, nor was the outside temperature recorded; however, the high temperatures in central Texas during this
time ranged from the mid-to-high 90s. The boy arrived at the hospital with an oral temperature of 102º F (39º C) and died 2
days later. The death was attributed to heatstroke.

Case 4. In a border town in Chihuahua State, Mexico, in August 2001, a man aged 21 years was found collapsed
and incoherent on the street. A witness reported that he had complained about abdominal pain and vomiting. He arrived at
an emergency department in New Mexico 3 hours after he was found. His rectal temperature was 105.7º F (40.9º C).
The patient had laboratory evidence of rhabdomyolysis, severe dehydration, and renal failure. Blood alcohol level and a screen
for drugs were negative. He died 3 hours after arrival at the hospital. Cause of death was attributed to hyperthermia due
to environmental heat exposure. High temperature at the border that day was 90º F (32º C).

United States

During 1979--1999, a total of 8,015 deaths in the United States was associated with excessive heat
exposure, 3,829 (48%) were "due to weather conditions," 377 (5%) were "of man-made origins" (i.e., heat generated in vehicles, kitchens,
boiler rooms, furnace rooms, and factories), and 3,809 (48%) were "of unspecified origin"
(3); 182 deaths per year (range: 54--651) were associated with excessive heat due to weather conditions. Of the 3,764 (98%) deaths specified as due to
weather conditions with a reported age (3), 142 (4%) occurred among children aged
<4 years, and 1,068 (28%) occurred among persons aged
>75 years (Figure 2).

Editorial Note:

The cases summarized in this report demonstrate risk factors for heat-related illness. Heat-related
illnesses include sunburn, heat cramps, heat rash, heat exhaustion, and heatstroke. Of these, the two most serious types of
heat-related illness are heat exhaustion and heatstroke, both of which can result in death. Symptoms of heat exhaustion include
heavy sweating, muscle cramps, fatigue, weakness, paleness, cold or clammy skin, dizziness, headache, nausea or vomiting,
and fainting. Untreated heat exhaustion can progress to heatstroke
(4). Even with prompt medical care, 15% of heatstroke
cases are fatal (5).

Symptoms of heatstroke include a high body temperature (oral temperature of
>103º F [>39.4º C] or a rectal
temperature of 106º F [41.1º C]); red, hot, dry skin and no sweating; rapid pulse; throbbing headache; dizziness; nausea;
confusion; disorientation; delirium; and coma. Heatstroke can occur in the absence of physical exertion. Infants, elderly persons,
socially isolated persons, bedridden persons, and persons with certain mental and chronic illnesses are at highest risk
(6,7). The elderly, especially those aged
>80 years, are susceptible to heat-related illness because they are less able to adjust to
physiologic changes (e.g., vasodilation) that occur with exposure to excessive heat and are more likely to be taking medication for
chronic illness (e.g., tranquilizers and anticholinergics) that increase the risk for heat-related illness
(5). Infants also are sensitive to heat. Conditions such as mild fever can progress quickly to heatstroke if heat stress occurs. Parents and other
caregivers should provide adequate hydration during summer months and refrain from dressing children too warmly
(5). Adults also should keep well hydrated during summer months.

Heatstroke also can occur in young, healthy persons who are exercising
(6), because physical exertion during hot
weather increases the likelihood of fainting and cramps caused by increased blood flow to the extremities
(5). Onset of heatstroke can be rapid and is considered a medical emergency.

The findings in this report are subject to at least three limitations. First, information on decedents is provided
by surrogates, who might not accurately describe characteristics or behavior of the decedents. Second, heat-related deaths due
to weather conditions or exposure to excessive natural heat might represent only a portion of actual heat-related deaths.
These deaths often are a diagnosis of exclusion and can be misclassified as a stroke or heart attack. Deaths attributed
to cardiovascular and respiratory disease increase following heat waves
(8). In addition, jurisdictions might use
different definitions of heat-related death. Finally, ICD-10 coding was introduced in 1999 and might not be comparable with
previous data for 1979--1998.

To reduce morbidity and mortality from heat-related illness, many cities have developed emergency response plans.
Local officials use meteorologic information and assess population characteristics to implement prevention strategies
(7). Spending time in an air-conditioned area is the strongest factor in preventing heat-related deaths
(1,9). The use of fans does not appear to be protective during periods of high heat and humidity
(1). If exposure to heat cannot be avoided, prevention
measures should include reducing or eliminating strenuous activities or rescheduling them for cooler parts of the day; drinking water
or nonalcoholic fluids frequently; taking cool showers frequently; wearing lightweight, light-colored, loose-fitting clothing;
and avoiding direct sunshine (9).

Public health messages disseminated to all age groups can make the public aware of the signs and symptoms of
heat-related illness. Prevention messages delivered as early as possible in the media can prevent heat-related illness, injury, and death
(1).

Because many heat-related illnesses and deaths occur among the elderly population, older persons should be encouraged
to take advantage of air-conditioned environments (e.g., shopping malls, senior centers, and public libraries) for part of the
day. Parents and other caregivers should be educated about the heat sensitivity of children aged <5 years
(5).

Acknowledgments

Case reports are based on data contributed by F Jordan, MD, Oklahoma Office of the Chief Medical Examiner. PJ McFeeley, MD,
M Markey, MD, New Mexico Office of the Medical Investigator and Univ of New Mexico School of Medicine. N Peerwani, MD,
L Anderson, Office of Chief of Medical Examiner, Tarrant County, Texas.

* The National Weather Service issues a heat advisory when the maximum daytime heat index is expected to be
>105º F (40.6º C) and the minimum
nighttime heat index is expected to be 80º F (26.7º C) for 2 or more consecutive days. The heat index takes into account air temperature and relative humidity and
indicates the actual feel of the temperature to the body.

 Underlying cause of death during 1979--1998 is classified according to the
International Classification of Disease, Ninth
Revision (ICD-9). Excessive heat has three categories: E900.0 "due to weather conditions," E900.1 "of man-made origins," and E900.9 "of unspecified origin." The data for 1999 are from ICD-10;
code X30 "exposure to excessive natural heat" was added to the 1979--1998 ICD-9 code E900.0, "excessive heat due to weather conditions."

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